A multi-lobal shaped pbo fiber, its preparation method and application

Abstract

This invention discloses a multi-lobed profiled PBO fiber, its preparation method, and its applications, belonging to the field of high-performance fiber technology. The multi-lobed profiled PBO fiber is obtained by extruding a PBO polymer solution through a spinneret with shaped orifices, followed by stretching, setting, washing, drying, and heat treatment. It meets the following performance specifications: morphological parameters: diameter 6–18 μm, cross-section of 3–10 lobes, profile >22%; thermal conductivity: 20–50 W / (m·K); coefficient of thermal expansion: -20–0 ppm / ℃; tensile modulus: 160 GPa–280 GPa. This invention addresses the problems in existing technologies where the thermal conductivity potential of PBO fibers is not fully utilized, profiled PBO fibers are limited to the pulp and paper industry, and there is a lack of multi-lobed profiled PBO fibers specifically for high thermal conductivity dielectric products.

Description

Technical Field

[0001] This invention belongs to the field of high-performance fiber technology, specifically relating to a multi-lobed irregular PBO fiber, its preparation method and application, and more specifically, a multi-lobed irregular PBO fiber suitable for preparing high thermal conductivity dielectric products (a resin composition containing multi-lobed irregular PBO fiber, a thermally conductive layer formed by curing the resin composition, and copper-clad laminates and printed circuit boards prepared from the thermally conductive layer, etc.), and its preparation method, as well as the application of the multi-lobed irregular PBO fiber in the preparation of high thermal conductivity dielectric products. Background Technology

[0002] With the explosive growth of the digital economy and artificial intelligence industry, computing centers, as the core of digital infrastructure, are rapidly developing towards ultra-high power density, high-density integration, and long-term continuous operation. As a key carrier of core components such as server motherboards, AI accelerator cards, and high-speed interconnect backplanes, the performance of the computing center's PCB directly determines its computing speed, stability, and energy consumption. Currently, the core technological bottlenecks facing computing center PCBs are concentrated in areas such as thermal management, structural stability, and signal integrity, with heat dissipation being particularly prominent: the power consumption of a single rack has soared from the traditional 5-10kW to over 50kW, the power consumption of a single AI server card has exceeded 700W, and the chip heat flux density has reached as high as 1000W / cm². 2 The vertical thermal conductivity of the current mainstream PCB substrate (FR-4) is only 0.2 to 3 W / (m·K), which means that heat cannot be dissipated quickly. This causes local hot spots to form around the chip, with temperatures reaching over 150°C. This can lead to chip frequency reduction, loss of computing power, and even thermal failure problems such as solder melting and substrate delamination.

[0003] Poly(p-phenylenebenzodioxazole) (PBO) fiber is a heterocyclic aromatic polymer fiber with high strength, high modulus, high thermal stability, low dielectric constant, and superior thermal conductivity compared to conventional organic fibers, making it an ideal reinforcing material for preparing high thermal conductivity dielectric products. Existing technologies have reported the use of PBO fibers in the interlayer of copper-clad laminates (CCLs). For example, Chinese patent CN120676528A discloses a CCL, its interlayer, its preparation method, and its application. This involves blending PBO fibers with glass fibers, weaving them, and then impregnating them with resin to obtain a CCL with both low dielectric loss and low coefficient of thermal expansion. However, this technology primarily utilizes the mechanical and dielectric advantages of PBO fibers and does not specifically optimize their thermal conductivity, particularly in constructing efficient thermally conductive networks. This is especially relevant given the high power consumption of computing center equipment (up to 1000 W / cm²). 2 For chips with high heat flux density, it is difficult to form a continuous, low thermal resistance heat conduction path in the thickness direction by relying solely on the conventional layup or weaving of existing circular cross-section PBO fibers, which cannot meet the heat dissipation requirements of ultra-high power density scenarios.

[0004] The cross-sectional shape of fibers has a decisive influence on their interfacial bonding, bulk density, and thermal conductivity network construction in composite materials. Through irregular design, the contact area between the fiber and the matrix can be significantly increased, improving the uniformity of fiber dispersion in the matrix and promoting denser "point-to-surface" or "surface-to-surface" contact between fibers, thereby constructing a more continuous three-dimensional thermal conductivity network. However, existing research on irregularly shaped PBO fibers is extremely limited. Chinese patent CN114959936A discloses a flat-oval cross-section PBO fiber and its preparation method, which prepares PBO fibers with a flat-oval cross-section through extrusion of elliptical, rectangular, or rhomboid spinning holes. This patent explicitly states that its flat-oval cross-section PBO fiber is intended for application in the pulp processing field, increasing the specific surface area to improve the adhesion of pulp, and thus for the preparation of high-performance PBO paper. This patent technology does not address the optimization of the fiber's thermal conductivity in the resin matrix, nor does it extend its application to high thermal conductivity dielectric products such as copper-clad laminates, PCBs, and other electronic packaging materials.

[0005] In addition, irregularly shaped cross-section fibers have been extensively studied in other fiber material fields. For example, Chinese patent CN116163030A discloses an irregularly shaped bicomponent composite fiber whose cross-sectional profile consists of a semi-circle and a multi-leaf shape. Utilizing the viscosity difference between high and low viscosity polymers, the fiber cross-section exhibits a structure with one side circular and the other side multi-leaf shaped. This fiber possesses good elasticity and quick-drying properties, making it suitable for textiles such as clothing. However, this patent relates to polyester or polyamide thermoplastic fibers, whose raw material system, spinning process (melt spinning), and application fields (textiles and apparel) are fundamentally different from PBO fibers (liquid crystal dry-jet wet spinning, used in high-performance composite materials). More importantly, this technology aims to achieve elasticity and quick-drying properties through irregular structures, without addressing the optimization of thermal conductivity or using the fibers to prepare high thermal conductivity dielectric products. Therefore, existing technology cannot provide any research basis for designing PBO fibers into multi-leaf irregular structures to improve the thermal conductivity of their thermally conductive dielectric products.

[0006] In summary, when applying PBO fibers to dielectric products to improve their thermal conductivity and thus solve the heat dissipation and structural stability bottlenecks faced by existing computing center PCBs, the following technical challenges still exist in this field: (1) Although PBO fiber has excellent thermal conductivity potential, existing application solutions have failed to fully utilize its thermal conductivity advantage and are difficult to meet the heat dissipation requirements of high heat flux density scenarios such as computing center PCB. (2) Currently, the publicly disclosed irregular PBO fibers (such as flat round type) are limited to the pulp and paper industry. Their design purpose is to increase the specific surface area to improve mechanical adhesion, rather than to build an efficient thermally conductive network, and they have not been involved in the preparation of high thermal conductivity dielectric products. (3) Other types of irregular fibers (such as bicomponent multi-leaf composite fibers) have completely different raw material systems, spinning processes and application purposes from the field of dielectric thermal conductivity, and cannot provide any technical reference.

[0007] Therefore, developing a multi-lobed, irregularly shaped PBO fiber specifically for high thermal conductivity dielectric products (including thermally conductive layers, copper-clad laminates, and PCBs), and constructing an efficient thermal conductivity pathway in the resin matrix through irregular cross-section design, to solve the technical problems of the underutilization of the thermal conductivity potential of PBO fibers and the lack of efficient thermal conductivity in high thermal conductivity dielectric products in the existing technology, has become an urgent direction for breakthroughs in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a multi-lobed irregular PBO fiber, its preparation method and application, in order to solve the problems in the prior art where the thermal conductivity potential of PBO fiber is not fully utilized, irregular PBO fibers are limited to the pulp and paper industry, and there is a lack of multi-lobed irregular PBO fibers specifically for high thermal conductivity dielectric products.

[0009] This invention is achieved through the following technical solution: a method for preparing multi-lobed irregular PBO fibers, wherein the multi-lobed irregular PBO fibers are obtained by extruding a PBO polymer solution through an irregularly shaped spinneret, followed by stretching, shaping, washing, drying, and heat treatment, and meet the following performance indicators: Morphological parameters: Diameter 6–18 μm, multi-leaved shape with 3–10 blades in cross-section, heterogeneity >22%; Thermal conductivity: 20–50 W / (m·K); Coefficient of thermal expansion: -20~0ppm / ℃; Tensile modulus: 160 GPa~280 GPa.

[0010] The solid content of the PBO polymer solution is 10-16%, and the intrinsic viscosity ranges from 18 to 30 dL / g.

[0011] The spinneret with irregular orifice has a multi-leaf structure with 3 to 10 blades, the blade length L is 0.08 to 0.40 mm, and the blade width W is 0.04 to 0.20 mm.

[0012] The stretching is spinneret stretching, with a stretch ratio controlled at 10–60, an extrusion temperature of 160–210℃, an extrusion pressure of 5.0–15.0 MPa, and a single-hole flow rate of 0.05–0.2 cc / min.

[0013] The shaping process involves feeding the stretched filaments into a coagulation bath, controlling the concentration of phosphoric acid in the coagulation bath to be 0–30%, the temperature of the coagulation bath to be 25–50°C, and the residence time to be 0.1–0.5 s.

[0014] The drying process is hot roller drying, with the temperature of the hot roller controlled at 60–400°C.

[0015] The heat treatment is carried out under nitrogen protection, with the treatment speed controlled at 20-250 m / min, the temperature at 450-650℃, and the tension at 1-3 cN / dtex.

[0016] Another technical solution of the present invention is to provide a multi-lobed irregular PBO fiber, which is prepared by the above-described preparation method.

[0017] Another technical solution of the present invention is to provide the application of the above-mentioned multi-lobed irregular PBO fiber in the preparation of high thermal conductivity dielectric products, wherein the high thermal conductivity dielectric products include: A resin composition containing the aforementioned multi-lobed, irregularly shaped PBO fibers; A thermally conductive layer formed by curing the resin composition; A copper-clad laminate prepared from the thermally conductive layer; and, A printed circuit board made from the copper-clad laminate.

[0018] The resin composition is prepared by impregnating a fabric of the multi-lobed PBO fiber, after modification, with a resin-containing impregnation solution.

[0019] The fabric made of the multi-leaf shaped PBO fiber is pure PBO fabric or a blended fabric made of one or more of glass fiber, quartz, polyimide, and aramid.

[0020] The fabric form of the pure PBO fabric or blended fabric is one or more combinations of unidirectional, plain weave, and widened weave.

[0021] The modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment.

[0022] The resin content in the impregnation solution is 35-70%, and the resin is selected from one or more of epoxy resin, hydrocarbon resin, cyanate ester, PPO resin, polyimide, phenolic resin and PTFE.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) This invention is the first to propose multi-leaf shaped PBO fibers specifically for high thermal conductivity dielectric products, filling a technological gap in this field. Existing shaped PBO fibers (such as flat round ones) are limited to the pulp and paper industry, and their design purpose is to increase the specific surface area to improve mechanical adhesion, rather than to build an efficient thermally conductive network. This invention significantly increases the specific surface area of ​​the fiber and its interfacial contact area with the resin matrix by designing the cross-section of the PBO fiber as a multi-leaf structure with 3 to 10 blades and controlling the degree of irregularity >22%. This allows the fiber to form a denser "point-to-surface" and "surface-to-surface" contact in the resin matrix, thereby constructing a continuous and stable three-dimensional thermally conductive network.

[0024] Tests have shown that the single-fiber thermal conductivity of the multi-lobed irregular PBO fiber of this invention can reach 20-50 W / (m·K), and the thermal conductivity of the thermally conductive layer prepared from it can reach 6-20 W / (m·K), which is more than an order of magnitude higher than that of the traditional FR-4 substrate and 2-3 times higher than that of conventional high thermal conductivity PCBs, providing a key material basis for efficient heat dissipation in high heat flux density scenarios.

[0025] (2) The multi-lobed irregular PBO fiber prepared by this invention has a negative coefficient of thermal expansion of -20 to 0 ppm / ℃. When combined with a resin matrix, it can effectively counteract the thermal expansion effect of the resin matrix, so that the coefficient of thermal expansion of the resulting thermally conductive layer can be adjusted to the range of -15 to 10 ppm / ℃, achieving a high degree of matching with the chip packaging material (coefficient of thermal expansion of about 5 ppm / ℃). This characteristic is particularly critical under high-temperature cyclic conditions such as PCBs in computing centers. It can significantly reduce the interface stress concentration caused by the mismatch of the coefficient of thermal expansion, effectively avoid thermal failure problems such as via cracking, circuit warping, and substrate delamination, and greatly improve the long-term operational reliability under high-density integration conditions.

[0026] (3) By coordinating the design of the multi-leaf cross section with the spinning process parameters, the efficient solidification and morphological maintenance of the irregular structure are achieved. During the spinning of PBO liquid crystal, oriented molecules are not easily deoriented. This invention utilizes this characteristic and controls key process parameters such as the spinneret draw ratio of 10-60, extrusion temperature of 160-210℃, coagulation bath temperature of 25-50℃, and residence time of 0.1-0.5s to ensure that the extruded multi-leaf filaments maintain a stable irregular structure after entering the coagulation bath. During the coagulation process, the fiber skin shrinks inward due to solvent removal. Due to the external water pressure, the indentation is deeper until the skin hardens, thus completely fixing the irregular shape. Tests show that the irregularity of the multi-leaf PBO fiber prepared by this invention is >22%, and the fiber diameter is uniform (6-18μm), with a tensile modulus as high as 160-280GPa, exhibiting both excellent mechanical properties and morphological stability.

[0027] (4) This invention not only provides a method for preparing multi-lobed irregular PBO fibers, but also clarifies their specific applications in resin compositions, thermally conductive layers, copper-clad laminates, and PCBs. By weaving the fibers of this invention into pure PBO cloth or blended cloth, and then modifying them (by at least one of plasma, irradiation, or silane coupling agent) and impregnating them in resin systems such as epoxy, hydrocarbon, cyanate ester, PPO, polyimide, phenolic, and PTFE, a thermally conductive layer and copper-clad laminate with high thermal conductivity, low expansion, high rigidity, and low dielectric loss can be obtained. The dielectric loss Df of this copper-clad laminate at a frequency of 10 GHz can be as low as below 0.002, the peel strength is ≥0.8 N / mm, and the solder heat resistance test (288℃, immersion in tin for 10 seconds, 6 cycles) shows no blistering or delamination, and no burrs when drilling holes, demonstrating excellent overall performance.

[0028] (5) This invention constructs a high-speed heat conduction channel in the in-plane direction using multi-leaf irregular PBO fibers, realizing a highly efficient thermal management design of "in-plane diffusion + vertical output". It can efficiently expand the local "point heat source" generated by the chip into a large-area "surface heat source", effectively reducing the hot spot temperature by more than 60°C, ensuring the long-term stable operation of computing center equipment under high heat flux density, and providing key material support for the high-quality development of the computing industry. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the spinning holes of the spinneret used in this invention.

[0030] Figure 2 This is a scanning electron microscope image of the five-lobed irregular PBO fiber described in this invention. Detailed Implementation

[0031] The invention's objective, technical solution, and beneficial effects will be further explained in detail below.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the claimed invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] This invention relates to a multi-lobed irregular PBO fiber, its preparation method, and its applications. The aim is to obtain a special fiber with ultra-high thermal conductivity, low coefficient of thermal expansion, and high mechanical strength by designing the cross-sectional shape of the PBO fiber to be irregular, specifically a multi-lobed shape with a diameter of 6–18 μm and a cross-section of 3–10 lobes, with an irregularity >22%. This fiber can then be applied to high thermal conductivity dielectric products, including but not limited to resin compositions, thermally conductive layers, copper-clad laminates, and printed circuit boards (PCBs). This addresses the technical challenges of underutilized thermal conductivity potential of PBO fibers, the limitation of irregular PBO fibers to pulp and paper production, and the lack of efficient thermally reinforcing materials for high thermal conductivity dielectric products.

[0034] Furthermore, the technical solution of the present invention can be summarized in detail as follows: (a) Multi-lobed irregular PBO fiber The multi-leaf shaped PBO fiber used in this invention is a high-performance fiber with a multi-leaf cross-section, which is prepared by a specific spinning process. The preparation process involves multiple steps such as extrusion, coagulation, stretching, washing, drying and heat treatment of PBO polymer solution. By adjusting the spinneret structure and process parameters, the fiber morphology and performance can be precisely controlled.

[0035] In a preferred embodiment, the preparation process is as follows: Polyphosphoric acid (PPA) was used as a solvent, and PBO fibers were prepared by dry-jet wet spinning in liquid crystal spinning. The solid content of the PBO polymer solution was 10-16%, and the intrinsic viscosity ranged from 18 to 30 dL / g. The spinning solution was extruded through a spinneret with irregularly shaped holes (e.g., ...). Figure 1 The extrusion temperature is 160–210℃. The spinneret has a multi-leaf structure with 3–10 blades, with a blade length L of 0.08–0.40 mm and a blade width W of 0.04–0.20 mm.

[0036] The extruded nascent filaments are stretched through a spinneret and then enter a coagulation bath. The stretch ratio is controlled at 10–60, the extrusion temperature at 160–210℃, the extrusion pressure at 5.0–15.0 MPa, and the single-hole flow rate at 0.05–0.2 cc / min. The concentration of phosphoric acid in the coagulation bath is 0–30%, the coagulation bath temperature is 25–50℃, and the residence time is 0.1–0.5 s. In the coagulation bath, the PPA solvent in the filaments diffuses into the coagulation bath, and the fiber morphology gradually becomes fixed.

[0037] like Figure 2 The image shown is a scanning electron microscope (SEM) image of PBO profiled fibers prepared using a five-hole spinneret (due to the extremely high strength of PBO, a smooth cross-section could not be obtained through sectioning, and observation was only possible from the outside). It is evident that the fibers exhibit distinct grooves and protruding ridges along their longitudinal extension, indicating successful preparation of the profiled PBO fibers. The maximum fiber diameter is approximately 18 μm, while the diameter of a circular PBO fiber with the same linear density is approximately 14 μm (since the minimum fiber diameter cannot be measured but is less than 14 μm, 14 μm is used here as an approximation).

[0038] PBO fiber irregularity = =(1-14 / 18)×100%>22% Furthermore, the coagulated fibers undergo multi-stage washing to remove residual phosphoric acid from the fibers. Subsequently, a multi-stage drying process is performed, with each stage dryer equipped with multiple hot rollers at temperatures ranging from 60 to 400°C. The fiber bundle is sequentially wound around these rollers, undergoing a stepped drying process at 60–150°C (stage one), 150–250°C (stage two), and 250–400°C (stage three) until the fiber moisture content is ≤5%.

[0039] After drying, the fibers undergo heat treatment under nitrogen protection to remove residual moisture and phosphoric acid and further improve the aggregated structure of the fibers. The heat treatment is carried out in a tube furnace, with the fiber bundle running slowly under a certain tension at a speed of 20–250 m / min. The heat treatment and nitrogen temperature is 450–650 °C, and the treatment tension is 1–3 cN / dtex. The resulting profiled PBO fibers must meet the following key indicators to ensure their excellent overall performance: Morphological parameters: The fiber diameter is 6-18 μm, the cross-section is multi-leaf shaped with 3-10 blades, and the anisotropy is greater than 22%. The high anisotropy greatly increases the specific surface area of ​​the fiber.

[0040] Thermal conductivity: The thermal conductivity of a single fiber is 20-50 W / (m·K), which is the basis for achieving high in-plane thermal conductivity of the thermal conductive layer.

[0041] Coefficient of thermal expansion: The coefficient of thermal expansion of a single fiber is -20 to 0 ppm / ℃. Its negative thermal expansion characteristics enable it to effectively control the overall thermal expansion behavior of the composite material after being combined with the resin matrix.

[0042] Tensile modulus: The tensile modulus of a single fiber is 160-280 GPa. The extremely high modulus provides excellent rigidity and dimensional stability to the final product.

[0043] (II) Application of multi-lobed profiled PBO fibers The multi-lobed PBO fiber prepared by the present invention can be used to prepare high thermal conductivity dielectric products, the high thermal conductivity dielectric products comprising: a resin composition containing the multi-lobed PBO fiber, a thermally conductive layer formed by curing the resin composition, a copper-clad laminate prepared from the thermally conductive layer; and a printed circuit board (PCB) prepared from the copper-clad laminate.

[0044] (1) For resin compositions In this invention, after the prepared multi-leaf shaped PBO fibers are spun into a fabric, they are modified and then impregnated in an impregnation solution containing resin to obtain a fiber prepreg, which is the resin composition.

[0045] The specific preparation method is as follows: First, the prepared profiled PBO fibers are woven into a fabric. The fabric structure can be selected from one or a combination of unidirectional, plain, and spread fabrics, depending on the needs. Unidirectional refers to fibers that are all in the same direction, which can reduce the thickness of a single layer of fabric. Plain weave refers to a weaving method where the warp and weft yarns interweave every other yarn in the perpendicular warp and weft directions, resulting in a more stable structure. Spread fabric refers to fabric made by spreading and thinning large bundles of fibers using airflow, ultrasound, and mechanical methods to obtain thinner yarns before weaving, which also reduces the thickness of a single layer of fabric. The choice of fabric type affects the thermal conductivity of the heat-conducting layer and the thickness of the single layer.

[0046] In a practical case, the prepared irregular PBO fibers can be woven into pure PBO fabric or blended with one or more of glass fiber, quartz, polyimide, and aramid to make a blended fabric.

[0047] Secondly, the woven fabric is modified to enhance the interfacial bonding between the fiber and the resin matrix. The modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment. For example, plasma treatment can employ online corona treatment with a power of 1–7 kW and a linear velocity of 3–20 m / min; irradiation treatment can use gamma rays or electron beams with a dose controlled at 50–300 KGy; silane coupling agent treatment involves immersing the fiber fabric in a solution containing a silane coupling agent (such as at least one of KH-550, KH-560, and KH-570) for 30 minutes while the solution is stirred to ensure uniformity, followed by air drying and baking at 120°C for 10–120 minutes. These treatments can introduce polar groups or increase surface roughness on the fiber surface, thereby improving the wettability and bonding strength between the fiber and the resin.

[0048] The modified fabric is then impregnated in an impregnation solution containing resin to obtain a fiber prepreg. The solid content of the resin in the impregnation solution is 35-70%. The resin used can be selected from epoxy resin, hydrocarbon resin, cyanate ester resin, PPO resin, polyimide, phenolic resin, and PTFE, depending on the requirements for dielectric properties, heat resistance, and bonding strength. In addition to resin, the impregnation solution may also contain curing agents (such as amine curing agents, acid anhydrides, or polythiols), fillers (such as silica or aluminum hydroxide), flame retardants (such as bromine-containing flame retardants, phosphorus-containing flame retardants, or aluminum hydroxide), accelerators (such as imidazole, thiourea, or triethylamine), and solvents (such as methyl ethyl ketone, acetone, or DMF), etc. The added substances or amounts are usually determined according to the physical property requirements of the actual application.

[0049] (2) For the heat-conducting layer In this invention, the fiber prepreg prepared above can be dried at 100-200°C for 2-10 minutes (drying time can be determined according to thickness, resin type, and solvent) to remove the solvent and place the resin in a specific state before semi-curing or complete curing, thereby obtaining a thermally conductive layer. More specifically, the drying is carried out in a multi-stage oven, with the temperature of each stage controlled at 60-100°C (stage 1), 100-150°C (stage 2), and 150-200°C (stage 3).

[0050] The thermally conductive layer prepared by the above method has the following performance indicators: In-plane thermal conductivity: 6–20 W / (m·K), which is due to the continuous thermal conduction pathways formed by the shaped fibers in the in-plane direction.

[0051] Coefficient of thermal expansion: -15~10ppm / ℃. By combining with PBO fiber with a negative coefficient of thermal expansion, the thermal expansion performance can be controlled, and it can achieve good thermal matching with chip packaging materials.

[0052] Flexural modulus: 10-40 GPa. The high modulus ensures the rigidity of the thermal conductive layer and even the entire copper clad laminate.

[0053] Tensile modulus: 160~280GPa, this index mainly inherits the high modulus characteristics of PBO fiber.

[0054] (3) For copper clad laminates In this invention, the above-mentioned heat-conducting layer can be used as an intermediate medium layer, and a first copper foil layer and a second copper foil layer can be covered on the upper and lower layers of the heat-conducting layer respectively to obtain a copper-clad laminate, the structure of which includes a first copper foil layer, a heat-conducting layer and a second copper foil layer stacked from top to bottom.

[0055] First copper foil layer: thickness is 18-105um.

[0056] Thermal conductive layer: The thickness is 50~4000um. This layer serves as the core reinforcement and thermal conductive layer, and its thickness can be adjusted according to the current carrying and heat dissipation requirements of the final PCB board.

[0057] The second copper foil layer has a thickness of 18–105 μm.

[0058] The preparation method of this copper-clad laminate is as follows: A first copper foil layer, a thermally conductive layer, and a second copper foil layer are stacked sequentially. Then, a surface protective layer precursor (such as kraft paper or a three-layer composite material) is applied to the outer surface of the first copper foil layer for cushioning and shaping. The stacked laminate is placed in a hot press and subjected to hot-pressing composite under specific temperature (170–280℃), pressure (1–6 MPa), and vacuum (-0.1 MPa) conditions. This ensures a tight bond between the layers and full resin curing, ultimately yielding the copper-clad laminate.

[0059] The resulting copper-clad laminate meets the following performance indicators: Peel strength: ≥0.8N / mm, indicating that the copper clad laminate made using PBO has good adhesion.

[0060] Solder heat resistance: After immersing in a tin bath at 288℃ for 10 seconds and repeating 6 times, it meets the requirement of no blistering or delamination, proving that it has excellent thermal shock resistance.

[0061] Drilling performance: The hole wall is smooth after drilling, with no obvious burrs, indicating that the material has good machinability.

[0062] Dielectric constant Dk: 2.5~3.8, which meets the performance requirements of the computing board.

[0063] Dielectric loss Df: ≤0.002@10GHz, indicating that it has extremely low loss and can be used in computing boards.

[0064] (4) For PCB boards In this invention, the copper-clad laminate described above can be used to prepare a high thermal conductivity computing center PCB board. Specifically, the copper-clad laminate can be processed using conventional PCB manufacturing processes (such as blanking, drilling, copper plating, electroplating, outer layer circuitry, solder masking, surface treatment, etc.) to finally obtain a high thermal conductivity computing center PCB board.

[0065] In a preferred embodiment, high-precision drilling (hole diameter tolerance ±0.01mm) is performed by ultraviolet laser drilling, and the vias are chemically deposited copper (copper layer thickness ≥0.8μm) and electroplated copper (plating layer thickness 15~25μm). After processes such as circuit etching, solder resist curing, and surface anti-oxidation treatment, an irregular A-fiber reinforced high thermal conductivity computing center PCB is produced.

[0066] The testing methods for performance indicators of fibers, thermally conductive layers, copper-clad laminates, and PCB boards in this invention are as follows: Fiber thermal conductivity: tested using laser flare method.

[0067] In-plane thermal conductivity: measured using the laser flare method.

[0068] Coefficient of thermal expansion: Tested using TMA equipment.

[0069] Peel strength: For testing methods, please refer to IPC-TM-650 2.4.8.

[0070] Solder heat resistance: For testing methods, please refer to IPC-TM-650 2.4.13.1.

[0071] Drilling performance: Tested using mechanical drilling.

[0072] Dielectric constant Dk: Detected using the SPDR method.

[0073] Dielectric loss Df: Detected using the SPDR method.

[0074] The specific embodiments of the present invention are described below with reference to examples. Of course, the scope of protection of the present invention is not limited to the following embodiments. In the following embodiments, the fiber preparation, modification treatment, impregnation process, hot pressing composite and other operations are all carried out using conventional technical means in the art unless otherwise specified.

[0075] Example 1: Five-lobed irregular PBO fiber The PBO polymer solution prepared according to the aforementioned method of the present invention has a solid content of 14.2%, an intrinsic viscosity range of 28 dL / g, an extrusion temperature of 178°C, a draw ratio of 20, an extrusion pressure of 6 MPa, and a single-hole flow rate of 0.05 cc / min. The concentration of phosphoric acid in the coagulation bath is 16%, the coagulation bath temperature is 35°C, and the residence time is 0.2 s. Drying is performed in stages at 150°C (primary stage), 250°C (secondary stage), and 400°C (tertiary stage). During heat treatment, the processing speed is 160 m / min. The heat treatment and nitrogen temperature is 600°C, and the treatment tension is 1.0 cN / dtex. It is then woven in a plain weave pattern.

[0076] In this embodiment, the fiber cross-section is pentaflop-shaped, the fiber diameter is approximately 18 μm, and the irregularity is calculated to be 22.22%, meeting the requirement of >22%. The single fiber thermal conductivity is 34 W / (m·K), the coefficient of thermal expansion is -16 ppm / ℃, and the tensile modulus is 265 GPa. These meet the performance indicators of the irregularly shaped PBO fiber described in this invention.

[0077] Example 2: Five-lobed irregular PBO fiber and glass fiber hybrid weaving The five-lobed irregular PBO fiber obtained in Example 1 was mixed with glass fiber (Shanghai Honghe Electronic Materials Co., Ltd. 2116) and woven in a plain weave pattern.

[0078] Comparative Example 1: Fiberglass E-cloth Commercially available electronic-grade glass fiber cloth (Shanghai Honghe Electronic Materials Co., Ltd. 2116).

[0079] Comparative Example 2: Fiberglass Q Cloth Commercially available quartz fiber cloth (Shanghai Honghe Electronic Materials Co., Ltd. FQW).

[0080] Comparative Example 3: Ordinary circular PBO fibers Referring to the preparation method and process parameters of the five-lobed irregular PBO fiber in Example 1, only the irregularly shaped spinneret was replaced with a spinneret with circular spinnerets. In this example, the fiber diameter is approximately 12 μm, with a circular cross-section. Its single fiber thermal conductivity is 20 W / (m·K), its coefficient of thermal expansion is -9 ppm / ℃, and its tensile modulus is 260 GPa.

[0081] Application examples: The fiber cloths of Examples 1, 2 and Comparative Examples 1 to 3 were processed into thermal conductive layers, copper-clad laminates and PCBs according to the processing method described in Table 1. Their performance indicators were tested according to the aforementioned test methods, and the results are shown in Table 2. This was to evaluate the comprehensive performance of different fiber cloths in terms of thermal conductivity, interfacial bonding performance, thermal expansion characteristics, dielectric properties and processing performance when used in thermal conductive layers and copper-clad laminates.

[0082] Modification treatment: γ-irradiation treatment was carried out in air at room temperature with a dose of 100 KGy; corona treatment was performed using an online corona treatment machine with a power of 3 KW and a line speed of 5 m / min; in the silane coupling agent treatment, KH-560 or KH-570 was used, and the mixture was soaked for 30 min, then removed and dried, and baked at 120℃ for 60 min.

[0083] Resin system: Epoxy resin system (bicycloisoprene epoxy resin) or hydrocarbon resin system (Ricon resin), with the resin content controlled at 60%. Filler: 60% BN ceramic filler or 60% silica (% is the solid percentage of filler in the resin, excluding solvent).

[0084] Preparation of thermal conductive layer: The modified fabric is immersed in the corresponding resin solution, the resin content is controlled, and then it is sent into a multi-stage drying oven and dried at 100-200℃ for 10 minutes to obtain the thermal conductive layer.

[0085] Copper-clad laminate preparation: The thermally conductive layer obtained above is used as the core layer, and an 18μm layer of electrolytic copper foil is placed on the top and bottom. The core layer is placed in a vacuum hot press and hot-pressed for 2 hours under the conditions of 210℃, 4MPa pressure and -0.1MPa vacuum to allow the resin to fully cure and obtain the copper-clad laminate.

[0086] PCB board preparation: The copper-clad laminate obtained above is used to prepare a high thermal conductivity computing power PCB board using conventional PCB processes.

[0087] Table 1. Different processing methods of each embodiment and comparative example

[0088] Table 2 Performance test results of thermally conductive layers / copper clad laminates prepared in each embodiment and comparative example

[0089] The test results in Table 2 show that: (1) Effect of modification treatment on interfacial bonding Comparing Comparative Examples 1 to 4 in Comparative Example 3, it can be seen that for ordinary round PBO fibers, different modification treatments are applied. Irradiation treatment (Comparative Example 3, Example 2) increased the peel strength of the copper-clad laminate from 0.63 N / mm (untreated, Comparative Example 3, Example 1) to 1.09 N / mm, an increase of 73%, significantly better than the 40% increase achieved by corona treatment (Comparative Example 3, Example 4). However, after irradiation treatment followed by silane coupling agent treatment (Comparative Example 3, Example 3, Example 3), the peel strength (1.06 N / mm) showed no significant difference compared to irradiation treatment alone, indicating that irradiation treatment itself can effectively improve the interfacial bonding between the fiber and the resin.

[0090] (2) The effect of irregularly shaped fibers on thermal conductivity Comparing Example 1 (1#) with Comparative Example 3 (2#), under the same epoxy resin system and irradiation treatment conditions, the copper-clad laminate prepared using five-lobed irregular PBO fibers (Example 1 (1#)) achieved an in-plane thermal conductivity of 11.6 W / (m·K), which is approximately 23.4% higher than the 9.4 W / (m·K) of ordinary circular PBO fibers (Comparative Example 3 (2#)). This indicates that the multi-lobed irregular structure significantly increases the specific surface area of ​​the fibers and its interfacial contact area with the resin matrix, which helps to construct a more continuous and denser three-dimensional thermally conductive network within the composite material, thereby fully utilizing the thermal conductivity potential of PBO fibers.

[0091] (3) The effect of filler on thermal conductivity Comparing Example 1 and Example 2, it can be seen that adding BN ceramic filler (Example 2) to the five-lobed PBO fiber can further increase the thermal conductivity to 14.5 W / (m·K), which reflects the synergistic effect of fiber and thermally conductive filler.

[0092] Comparing Example 1# with Example 1#, it can be seen that adding BN ceramic filler (Example 1#) to the five-lobed PBO fiber further increases the in-plane thermal conductivity to 14.5 W / (m·K), which is about 25% higher than Example 1# (11.6 W / (m·K)) without filler. This indicates a significant synergistic effect between the multi-lobed PBO fiber and the high thermal conductivity filler.

[0093] (5) The effect of different resin systems on dielectric properties Comparison of the various embodiments and comparative examples shows that after adopting the hydrocarbon resin system, the dielectric loss Df of the copper clad laminate is significantly reduced from 0.011-0.016 to below 0.001, and the dielectric constant Dk is also reduced, making it more suitable for high-frequency applications.

[0094] Comparison of the various embodiments and comparative examples shows that the dielectric loss Df of the copper-clad laminate is significantly reduced after adopting the hydrocarbon resin system. In the five-lobed PBO fiber system, the Df of the hydrocarbon resin (3# in Example 1) is 0.00089, which is about 92% lower than that of the epoxy resin (2# in Example 1) which is 0.01131. In the five-lobed PBO and glass fiber hybrid system, the Df of the hydrocarbon resin (2# in Example 2) is 0.00121, which is about 90% lower than that of the epoxy resin (1# in Example 2) which is 0.01212. At the same time, the dielectric constant Dk also decreases, making it more suitable for high-frequency applications. This indicates that the multi-lobed PBO fiber of the present invention can be adapted to various resin systems, and the dielectric properties can be flexibly adjusted according to application requirements.

[0095] (6) Regulation of thermal expansion coefficient by PBO fiber Comparison of the various embodiments and comparative examples shows that the coefficient of thermal expansion (CTE) of the copper clad laminate significantly decreased after the introduction of multi-lobed PBO fibers. In Embodiment 1, 2# and 3# using pure five-lobed PBO fibers had CTEs of -3.5 ppm / ℃ and -3.7 ppm / ℃, respectively, both exhibiting excellent negative thermal expansion characteristics. In Comparative Example 3, 5# using pure five-lobed PBO fibers had a CTE of -4.5 ppm / ℃, also exhibiting negative thermal expansion, but its in-plane thermal conductivity (9.2 W / (m·K)) was significantly lower than that of 2# (14.5 W / (m·K)) and 3# (11.4 W / (m·K)) in Embodiment 1, indicating that the multi-lobed structure significantly improved thermal conductivity while maintaining excellent negative thermal expansion characteristics.

[0096] The CTE of the blended fabrics (1# and 2# in Example 2) is between that of pure PBO and pure glass fiber, at 3.7 ppm / ℃ and 2.1 ppm / ℃ respectively, which provides the possibility for on-demand adjustment of performance.

[0097] In summary, this invention, by employing five-lobed irregular PBO fibers combined with appropriate modification treatments and resin systems, can produce copper-clad laminates that possess high thermal conductivity, low expansion, high rigidity, and low dielectric loss. Compared to ordinary circular PBO fibers, the five-lobed irregular PBO fibers, due to their multi-lobed cross-sectional structure, significantly increase the specific surface area and interfacial contact area, constructing a more continuous and efficient three-dimensional thermal conductive network in the composite material, thereby improving the in-plane thermal conductivity by approximately 23.4%. Among them, #2 in Example 1 excels in pursuing high thermal conductivity, with a thermal conductivity of 14.5 W / (m·K), while maintaining a negative coefficient of thermal expansion (-3.5 ppm / ℃) and excellent dielectric properties (Df=0.01131); while #3 in Example 1 maintains high thermal conductivity (11.4 W / (m·K)) while achieving extremely low dielectric loss (Df<0.001@10GHz) and ultra-low negative coefficient of thermal expansion (-3.7 ppm / ℃), making it an implementation scheme with excellent overall performance.

[0098] Furthermore, the multi-lobed, irregularly shaped PBO fiber of this invention is compatible with various resin systems (epoxy, hydrocarbon, etc.) and exhibits a significant synergistic effect with thermally conductive fillers (such as BN), providing flexible material selection options for different application scenarios. The PCB board made from the copper-clad laminate described in this invention can precisely meet the stringent requirements of computing centers for high-performance motherboards, accelerator cards, and other core components. This board can rapidly dissipate localized hotspot heat generated by the chip along the board surface, thereby effectively reducing hotspot temperatures. Its coefficient of thermal expansion is highly matched with the chip packaging material, significantly improving interconnect reliability under high-density packaging conditions, while also effectively ensuring the integrity and low attenuation of high-frequency signals during transmission.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing multi-lobed heteromorphic PBO fibers, characterized in that: The multi-lobed profiled PBO fiber is produced by extruding a PBO polymer solution through a spinneret with shaped orifices, followed by stretching, setting, washing, drying, and heat treatment, and meets the following performance indicators: Morphological parameters: Diameter 6–18 μm, multi-leaved shape with 3–10 blades in cross-section, heterogeneity >22%; Thermal conductivity: 20–50 W / (m·K); Coefficient of thermal expansion: -20~0ppm / ℃; Tensile modulus: 160 GPa~280 GPa.

2. The preparation method according to claim 1, characterized in that: The solid content of the PBO polymer solution is 10-16%, and the intrinsic viscosity ranges from 18 to 30 dL / g.

3. The preparation method according to claim 1, characterized in that: The spinneret with irregular orifice has a multi-leaf structure with 3 to 10 blades, the blade length L is 0.08 to 0.40 mm, and the blade width W is 0.04 to 0.20 mm.

4. The preparation method according to claim 1, characterized in that: The stretching is spinneret stretching, with a stretch ratio controlled at 10–60, an extrusion temperature of 160–210℃, an extrusion pressure of 5.0–15.0 MPa, and a single-hole flow rate of 0.05–0.2 cc / min.

5. The preparation method according to claim 1, characterized in that: The shaping process involves feeding the stretched filaments into a coagulation bath, controlling the concentration of phosphoric acid in the coagulation bath to be 0–30%, the temperature of the coagulation bath to be 25–50°C, and the residence time to be 0.1–0.5 s.

6. The preparation method according to claim 1, characterized in that: The drying process is hot roller drying, with the temperature of the hot roller controlled at 60–400°C.

7. The preparation method according to claim 1, characterized in that: The heat treatment is carried out under nitrogen protection, with the treatment speed controlled at 20-250 m / min, the temperature at 450-650℃, and the tension at 1-3 cN / dtex.

8. A multi-lobed, irregularly shaped PBO fiber, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the multi-lobed irregular PBO fiber as described in claim 8 in the preparation of high thermal conductivity dielectric products, characterized in that: The high thermal conductivity dielectric product includes: A resin composition containing the aforementioned multi-lobed, irregularly shaped PBO fibers; A thermally conductive layer formed by curing the resin composition; A copper-clad laminate prepared from the thermally conductive layer; and, A printed circuit board made from the copper-clad laminate.

10. The application according to claim 9, characterized in that: The resin composition is prepared by impregnating a fabric of the multi-lobed PBO fiber, after modification, with a resin-containing impregnation solution.

11. The application according to claim 10, characterized in that: The fabric made of the multi-leaf shaped PBO fiber is pure PBO fabric or a blended fabric made of one or more of glass fiber, quartz, polyimide, and aramid.

12. The application according to claim 10, characterized in that: The fabric form of the pure PBO fabric or blended fabric is one or more combinations of unidirectional, plain weave, and widened weave.

13. The application according to claim 10, characterized in that: The modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment.

14. The application according to claim 10, characterized in that: The resin content in the impregnation solution is 35-70%, and the resin is selected from one or more of epoxy resin, hydrocarbon resin, cyanate ester, PPO resin, polyimide, phenolic resin and PTFE.

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